Spatially Variable Response of Antarctica's Ice Sheets to Orbital Forcing During the Pliocene

Variations in Earth’s orbit pace global ice-volume/sea-level changes, but the variability in the response for different sectors of the Antarctic Ice Sheet (AIS) to orbitally-forced climate change remains unclear. We present geological records of iceberg-rafted debris (IBRD) and other proxies from locations adjacent to the West Antarctic Ice Sheet (WAIS) and East Antarctic Ice Sheet (EAIS) spanning ~3.3-2.3 Ma. Iceberg calving events from the WAIS recorded in Ross Sea sediment cores show a linear response to orbital forcing at timescales corresponding to obliquity (40 kyr) and precession (23-19 kyr) modulated by eccentricity (100 kyr). This contrasts with records adjacent to the EAIS, which lack obliquity pacing. Geological data and ice sheet model sensitivity tests show the WAIS is highly dynamic and responsive to oceanic melt driven by changes in Southern Ocean circulation, together with atmospheric forcing through variations in local insolation. Conversely, the EAIS appears less responsive to oceanic forcing, despite being the dominant source of meltwater to the global ocean during the mid-Pliocene. Our results imply a significant role for atmospheric warming on mid-Pliocene sea-level.